1. Technical Field
The present disclosure generally relates to a method and an apparatus for notifying activations of extended access barring (EAB) and updates of EAB information in the field of Long Term Evolution (LTE) wireless communication systems.
2. Related Art
Machine Type Communication (MTC) is a novel communication technique among machines and often involves communications either with very limited human interventions or completely without. Implementations of MTCs may be evident in the practical applications such as metering, transportation, health care system, remote maintenance, and etc.
The MTC has several characteristics: First of all, the population density of MTC devices is generally much higher than human to human (H2H) communication devices. Second of all, MTC devices are usually considered to have lower communication priority than H2H devices. Third of all, the MTC devices can be behaviorally unpredictable as they may not exhibit a regular pattern as to when they may require network resources. Based on these three characteristics, if an enormous quantity of MTC devices attempt to attach to a network, the MTC devices would easily consume all the network resources and cause overloading to the network. In order to prevent network congestions or overloading, a measure to curtail this type of problem is required.
For the 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) communication system, the Extended Access Barring (EAB) scheme has been introduced to prevent congestion or overload in the Radio access network (RAN) or in the Core Network (CN). EAB is a mechanism for which random access (RA) attempts from MTC devices can be controlled. In LTE, each user equipment (UE) may be classified into one of the Access Classes (AC) between 0 to 9. When a LTE resource channel, the Physical Random Access Channel (PRACH), is too congested, the EAB scheme could mitigate PRACH congestion by barring some ACs of MTC devices from accessing the network. EAB parameters are located in the System Information Blocks (SIBs) of the System Information (SI) which is broadcasted periodically by the LTE Network through the Broadcast Control Channel (BCCH). Since the EAB parameters are treated as a kind of System Information (SI) in LTE, it would need to be updated within the SI according to a prescribed updating mechanism. However, the prescribed SI updating mechanism possesses shortcomings in which the updating mechanism is rendered ineffective in coping with the network overload problem.
Specifically, the SI in LTE cannot be modified at any time. Only at each Modification Period Boundary (MPB) would the SI be allowed to be modified. Supposedly if the MPB is set to be 640 milliseconds (ms), the SI would then only be allowed itself to be modified once every 640 ms. Based on the MTC characteristics as previously mentioned, if an enormous quantity of MTC devices were to perform RA attempts, the EAB scheme cannot be enacted soon enough to curtail PRACH overloads since the EAB parameters cannot be immediately updated according to the currently prescribed updating mechanism.
To order to circumvent the restriction caused by the MPB, two main schools of thoughts have been proposed for LTE. The first proposed method is mandate reading of the EAB information for each MTC before an access. The second proposed method is notification of EAB information update through paging.
For the first proposed method, the network would not be restricted by the MPB as the network could update the EAB parameters any time at any EAB-SIB, the specific system information block of the SIBs which contains the EAB System Information. The network could update the EAB parameters without any notifications to the MTC devices. However, the MTC devices would be required to obtain the EAB-SIB before any attempts to access the network.
For the second proposed method, the network also would not be restricted by the MPB as the EAB information could be updated any time at any EAB-SIB. The difference from the first proposed method is that the network is required to notify the change of EAB parameters through paging, which means that the MTC would be paged by the network paging channel. For the second proposed method, any EAB status change would trigger the network to send a paging message containing an EAB change notification. The EAB status change may include the EAB enable, any EAB parameters change, or the EAB disable. When the EAB status change is detected from a paging message, the MTC would only know that the EAB status has been changed through being able to distinguish what kind of change has been implemented. Therefore, in order to acquire the latest EAB status, any MTC device which receives the page containing the EAB change notification would be requested to acquire the EAB-SIB immediately.
For example, if the EAB is enabled by a base station (BS) or eNodeB (eNB), a paging message containing EAB change indicator which equals true would be transmitted to any MTC device within a receiving range. When the paging message is received by a MTC device, the EAB-SIB would immediately be acquired. If the EAB parameter is changed by an eNB, a paging message containing EAB change indicator which equals true would also be transmitted to any MTC device within a receiving range and caused the MTC devices to acquire the EAB-SIB. Similarly, if the EAB is disabled by an eNB, a paging message containing EAB change indicator which equals true would also be transmitted to any MTC device within a receiving range and caused the MTC devices to acquire the EAB-SIB. But if a normal paging, meaning paging not involving EAB, is made, the EAB change indicator would equal false, since the EAB change indicator would only indicate a EAB status change.
Comparing both proposed update mechanisms, the first proposed method has an advantage of being able to modify the EAB information without having to first notify MTC devices. The other advantage is that there would be no impact on H2H UEs and on MTC devices which do not attempt to access the network. However, the disadvantage is that the MTC devices would have to acquire EAB-SIB whenever they perform a RA to the network. Since EAB might be a relatively rare event, the MTC devices would consume power needlessly only to find out that the EAB has not been enacted. Also acquiring the EAB information before RA attempt would cause some degrees of synchronous access problem which will happen after MTC devices acquire EAB-SIB and discover that the EAB is still disabled or discover that they are not actually barred by the EAB.
On the other hand, for the second proposed method, has an advantage of not causing synchronous access problems and unnecessary SIB acquisitions when EAB is disabled. However, a disadvantage is that there would be a high paging overhead since the network would use paging messages to notify each EAB update to MTC devices, and also the network might change EAB parameters frequently such as to rotate barred access classes or to remove the barring in gradual steps. Also it would not be necessary to require all MTC devices to immediate obtain EAB information after EAB status change has been detected through paging messages because the MTC devices might not actually need the EAB information and also not all MTC devices would want to access the network.
Therefore, since it appears that both the first and the second proposed method are not completely satisfactory, another solution would be required to alleviate the shortcomings of current proposals, such as a solution to resolve the problems of high paging overhead and non-necessary impact on the MTC devices when paging messages are used.